There are known methods for concealing data to be stored in a database, including, among others: (1) cryptography using transparent encryption, (2) cryptography using searchable encryption and the like, and (3) cryptography using fully homomorphic encryption.
(1) Transparent encryption conceals data stored in a database by encrypting the data before storing the data in the database (for example, see Non-patent literature 1).
(2) Cryptography using searchable encryption and the like performs certain processing on ciphertexts to allow data to be searched for or to be subjected to manipulations that depend on encryption schemes while the data is kept concealed (for example, see Non-patent literature 2).
(3) Cryptography using fully homomorphic encryption performs arbitrary processing on data to allow the data to be manipulated while the data is kept concealed (for example, see Non-patent literature 3).